A process and apparatus for the prevention of ice formation in tunnels

ABSTRACT

Processes and devices for the prevention of ice formation in tunnels, especially road and railway tunnels, mountain cuttings and the like, by the supply of heat from the outside to rock faces where the formation of ice normally occurs. More particularly, this involves installing electrical heating means distributed in a self-supporting manner in individual bores formed in a rock face substantially at right angles to a boundary surface with the air and heating a layer of rock between the air and rear-lying masses of rock to a temperature higher than the temperature at said boundary surface and lower than the temperature of said rear-lying rock masses.

United States Patent Moldskred [54] A PROCESS AND APPARATUS FOR THEPREVENTION OF IC FORMATION IN TUNNELS [72] Inventor: Oddmund Moldskred,Brakehaugen, 5050 Nesttun, Norway [22] Filed: Dec. 7, 1970 [21]Appl.No.: 95,452

[52] U.S. Cl. ...2l9/213, 6l/45 R [5l] ..H05b 3/00 [58] Field ofSearch..2l9/200, 201, 213, 345;

61/36 A, 45 B, 45 R; 299/l4 1451 June 6,1972

Primary Examiner-C. L. Albritton Allurneys- Kenyon& Kenyon Reilly Carr &Chapin s7 ABSTRACT Processes and devices for the prevention of iceformation in tunnels, especially road and railway tunnels, mountaincuttings and the like, by the supply of heat from the outside to rockfaces where the formation of ice normally occurs. More particularly,this involves installing electrical heating means distributed in aself-supporting manner in individual bores formed in a rock facesubstantially at right angles to a boundary surface with the air andheating a layer of rock between the air and rear-lying masses of rock toa temperature higher than the temperature at said boundary surface andlower than the temperature of said rear-lying rock masses.

27 Claims, 6 Drawing Figures PATENTEDJUN s 1972 3, 668 368 SHEET 10F 2INVENTOR: ODDM um: MOLDSKFPED 1 PROCESS APPARATUS'FORTHE PREVENTION OFICE FORMATION IN TUNNEIS This invention relates, in general, to aprocess for preventingthe forrnationof ice in tunnels, especially roadand railway tunnels, andsimilar mountain cuttings by supplying heat fromthe outside to that portion of the mountain where ice fon'nation occursand devices for carrying out theprocess.

It has previouslybeen proposed, for-example,in US. Pat.

No. 2,018,293, toprovide a heating arrangement designed for an upwardlydirected surface which is designed to betrodden on or driven on by heavytrafiic. The upwardly directed surface is adapted by heating of theground to be kept free of snow and ice. The heating elements are, insuch circumstances, arranged at a suitable level below the top surfaceinserted in a suitable road material and. are adapted to be suppliedwith a suflicient amount of heat to not only'prevent ice formation onthe roadway but also to supply sufficient heat to continuously melt snowand possibly ice formations on the roadway. In orderto achieve the bestpossible heating efiect the heating elements are disposed in slingsparallel to the surface which is to be heated. Such a solution iscertainlynot practicable for tunnel walls and similar rock faces.Firstly, the placing of the heating elements in slings parallel to thesurface which is to be heated gives, from a heat-technical view, anuneconomic solution .both in the case of heat elements ar ranged in amoulding layer outside the rock face which is to be heated and in thecase of heatingelements arranged freely outside the rock face. in thefirst-mentioned instance, where the heating elements are to be insertedin a moulding layer.

over the whole tunnel archway .or the like, production and possiblerepair costs are prohibitively expensive without giving a satisfactorypractical solution. The moulding shell which is erected outside the rockface cannot provide an effective seal against water leakage fromrear-lying rock portions and will thus be subject to breaking up.Hitherto, experience with such moulding shells has not been especiallygood. In the second instance, where the heating elements are arrangedfree-lying outside the rock face, production and maintenance costs arecertainly relatively low, but as a consequence of the outside aircirculating past, the loss of heat to the outside air isdisproportionately high.

in many mountain cuttings and overhangs, and in most tunnels for railandwheel-going vehicles in areas having especially lowwinter temperatures,ice formation presents a serious disadvantage and danger for thetraffic. Such ice fon'nation is especially prominent in water-carryingcrevices in the .heat capacity. Furthermore,

wards from the mass of the mountain, flowing,

and ice formation can be avoided in a relatively simple and easy manner.

It is still another object of the invention to provide additionalimprovements in the heating and arrangements for performing the process.

A main concept of the present invention is the recognition of thefactthat'themass of the mountain always has a relativelyhigh backgroundtemperature, that is to say of the order of magnitude of from2. to 8 C,and with an almost inexhaustible the mountain mass is a relativelygoodheat conductor, of an order of magnitude of four times the heatconductivity of water. The consequence of this is that onlythe outermostlayer of the mountain rock mass is cooled below 0- C. By cooling downthe outer portion of the rock mass, there will thus alwaystake place aflow of heat from the rear-lying rock massesand this will involve thezero centigrade depth beinggdisplaced comparatively little inwards intothe mountain, even after long cold periods. The present invention isbased upon the afore-mentioned recognition, the aim being to utilize thestream of heat from the rear-lying rock masses as much as possible. Theaim is only to heat the outer layer of a rock face to a temperatureabove zero, but nevertheless lower than the temperature of therear-lying rock masses so that the flow of heat from such rear-lyingmasses is not turned but, on the contrary, so that such a flow of heatis maintained to a certain, though reduced, extent, the most substantialloss of heat at the outermost layer of all of the mountain only beingcompensated for, thereby preventing the formation of ice on the outersurface. The aim is to keep the water which trickles outnot only in themountainbut also outside the latter.

A process according to the invention is characterized in that theexposed rock faces are heated by the placing of distributed heaters in aself-supporting manner in bores substantially at right angles to themain boundary surface to the air, a rock face between the air and therear-lying rock masses being heated to a temperature higher than thetemperature of the boundary surface to the air but lower than thetemperature of the rear-lying rock masses, so that the heating cancounteract the transport of heat from the rear-lying rock masses towardsthe main boundary surface to the air, and from the said layer towardsthe rear-lying rock masses. 7

In addition to the heat-technical advantages which are achievedaccording to the invention by introducing the distributed heaterssubstantially at right angles to the outer surface so as to heat therebythe rock masses to a certain layer depth, there are obtained by themethod according to the inmountain, and loosened ice and stone blocksoften cause significant material damage and can in certain circumstancesbe a risk'to human safety.

in general, problems arise with water dripping in tunnels and mountaincuttings, both in the winter and the summer. I The biggest disadvantagesoccur on conventional gravel or oil- 'gravelled roads but even onasphalt or concrete roads, the problems can be rather large since theconstant dripping of I water hollows out the surface of the road and inaddition the water is distributed over larger portions of the roadway.During the winter, such water dripping results in the build up ofvention special constructional advantages. A series of bores can thus bebored out in the rock face with conventional boring equipment andthereafter the heaters can be mounted in such bores in a self-supportingmanner so that there is obtained a simple and secure fixing of theheaters in a ready way. it should be clearly evident that the mountingof the heating unit can be carried out, according to the circumstances,in an especially easy and inexpensive manner.

It is preferred, according to the invention, that the heaters aredisposed at a mutual distance of between 30 and cm, preferably about 50cm. With a mutual distance of about 50 cm, there is achieved anespecially uniform dispersion of the quantity of heat from the heatersover the whole area between the heaters. I

it is apparent that the quantity of heat supplied can be regulated byplacing the heaters at larger or smaller distances from each other byrespectively using stronger or weaker heating efl'ects from the heaters.An actual heating efiect can be, for example, about 50 W/m when heatersof 14 W areutilized. According to the invention a satisfactory heatingeffect is achieved with heaters of, for example, 7 W.

The present invention comprises furthermore devices for carrying out themethod and such a device is characterized by electrical heating meansdimensioned so as to be installed and received so as to be almost fullypushed directly in individual bores in the rock face in aself-supporting manner by means of suitable locating means.

The heater can be designed so as to be received in the bore inserted ina heat-conducting moulding mass which is introduced directly into thebore, according to a first embodiment. According to a second embodimentthe heater can be enclosed in an outer jacket of elastic,heat-conducting material so as to be receivable as a unit in the boreina self-supporting manner.

By heating the tunnel archway or similar overhanging rock face by theaforesaid method and/or by means of the aforesaid devices of theinvention, it has been possible to avoid the formation of ice on thetunnel archway or the overhanging rock face with a relatively smallamount of heat, but as a consequence of the dripping of water from theheated tunnel archway or the overhanging rock face, there have resulted,nevertheless, some difficulties due to the build up of ice on the groundbelow the tunnel archway or below the overhanging rock face.

According to another embodiment of the invention a process forpreventing the formation of ice in tunnels and similar rock faces bysupplying heat from the outside to the rock face comprises covering theexposed rock face in a tunnel archway or in a similar rock face againstthe outside air with a cloth, fluid-tight and, preferably, alsogas-tight facing material to form a liquid-conducting layer and atemperature barring or blocking layer between the rock face and thecloth material, the latter, with a suitable intermediate space, beinganchored to the rock face via electrical heating means which are fixedin individual bores in the rock face.

By the afore-mentioned solution, the water dripping from the rock facecan be led in a controlled manner to the fringes of the roadway in thetunnel or the like and, if desired, can be led away in a frost-proofdrainage ditch or another suitable collecting means. Furthermore, bymeans of the said facing, a substantial flow of cold air past thecovered rock face can be avoided so that the need for heat to avoid theformation of ice on the covered rock face can be additionally stronglyreduced.

The process according to the invention is from the procedural point ofview especially advantageous in that the heating means are first securedin the rock face with free outwardly projecting coupling ends andthereafter the cloth material is threaded in position on the couplingends and finally secured in place by arranging current-conducting meansoutside the cloth material in current-conducting connection with thecoupling ends associated with the heating means.

It is preferred to utilize relatively rigid current-conducting meansbetween the distributed heaters, the current-conducting means serving assupporting means and/or carrying means for the cloth material. In thisway, the possible formation of ice which will occur on the stoppage ofcurrent or for other reasons in the layer between the cloth material andthe covered rock face, is collected up in an effective manner by thecooperating support of the cloth material and the currentconductingmeans. Similarly stones which have come free from the covered mountainportion can be gathered up in the cloth material.

Moreover, it is preferred to utilize a cloth material with alight-reflecting surface directed outwardly from the covered rock face.In this way, there can be combined in one and the same construction, theafore-mentioned advantages with an especially favorable light-technicalsolution. It should be understood that the term cloth in thisspecification also embraces an appropriate cloth-like material.

A device for carrying out the process according to the invention ischaracterized by a cloth, fluid-tight and preferably also gas-tightfacing material being anchored, with a suitable intermediate space, tothe rock face via electrical heating means which are fixed in bores inthe rock face to form a liquid-conducting layer and a temperaturebarring or blocking layer between the rock face and the cloth material.

It is preferred to employ current-conducting means consisting of rigidcurrent-conducting rails of metal, preferably of reinforcing steel,which are welded to or are fastened in current-conducting connection tothe heating means in another suitable way. I

F urthermore,it is preferred that the heaters consist of a barorloop-shaped heating element of metal rod, such as reinforcing steel,inserted in a heat-conducting moulding mass directly in a bore in therock face.

In order that the invention can be more clearly understood, convenientembodiments thereof will now be described, by way of example, withreference to the accompanying drawings in which:

FIG. 1 is a section through a tunnel,

FIG. 2 is a section showing a detail of a portion of the tunnel roof ofFIG. 1 with heating cartridges inserted,

FIG. 3 is a diagram showing the temperature distribution along the lineA A of FIG. 2 with and without the supply of extra heat,

FIG. 4 is a section of a tunnel having heaters located only in theuppermost portion of the tunnel archway,

FIG. 5 is a vertical section illustrating a detail in the slit betweentwo current-conducting means and a heater and an associated clothmaterial, and

FIG. 6 is a section at right angles to the section of FIG. 2.

In the tunnel of FIG. 1, the low air temperature t causesa cooling ofthe mass of rock which has a temperature in the deeper layers, that isto say at a certain distance from the tunnel surface. The airtemperature in the tunnel can, disregarding extreme values, go down to-10 to 20 C, while the temperature in the heart of the mountain will beup to 10 C at the actual mountain depths. This temperature is dependent,however, upon the region and the height above sea-level. There wilLthusoccur a flow of heat energy in towards the tunnel opening, that is tosay in the direction of the arrow of FIG. 1.

In FIG. 2, there is shown a section of a tunnel roof with, anarrangement for preventing ice formation in the form of heatingcartridges 11 which are inserted in holes 12 in the rock. The holes arebored in advance in the usual way and can be from 15 to 30 cm deep andhave a diameter of from 2.5 to 5 cm, depending upon the dimensions ofthe heating cartridges.

The main portion of the heating cartridges 1 1 is the barshaped portion13 which receives the heating element. The bar-shaped portion 13 ispreferably of cylindrical form and fits in the bore in the rock. Theheating cartridge 11 comprises besides a coupling head 14, theindividual heating cartridges being coupled to the electrical supplysystem in an appropriate series or parallel coupling by means onconnection leads 15.

The heating element per se, which is not shown, can be designed in anumber of known ways, for example as a stocking of resistance wire.

In view of the low surface temperature which has necessarily shownitself, the heating element can be enclosed in a cheap and easily madeinsulation material. The outer jacket of the heating cartridge isadvantageously formed from an elastic and shock-resistant material, suchas rubber. The design of the coupling portion and other details of thecartridge is conventional and will, therefore, not be discussed furtherhere.

The outer surface of the heating cartridge can be made elastic, forexample, by arranging yielding ribs with a slightly larger diameter thanthe light opening of the hole 12, whereby the heating cartridge can beheld in place without special auxiliary means. However, the best resultscan be achieved if it is cast in a moulding material 16 as shown. Inthis way, air pockets between the heating cartridge and the rock whichcan reduce the heat transfer are avoided. The moulding material servessimultaneously as a binding agent and holds the heating cartridgesecurely in position.

By virtue of the good heat-conducting relationship between the source ofheat and the heat consumer, that is to say between the heating cartridgeand the air of the tunnel, the arrangement according to the inventionoperates with a low thermal inertia. The heating element only needs tobe coupled in, in the time-space in which the temperature is at itslowest. The consumption of energy and the operation expensescan,therefore, be reduced to a low level.

The cost of procuring the heating equipment and especially mounting thelatter will be low just the same since the heating .Figure,

cartridges can be produced by machine and hence reasonably and themounting only involves the boring of holes and introduction of heatingcartridges and the setting up of supply lines. The necessary controlequipment can be very limited.

The controlcan be based in a known manner on a thermostatic coupling.For example, a thermostat or a combination of thermostats can be.employed, which besides reacting at the temperature of the air in thetunnel or on the outside, also takes into account the temperature at oneor more predetermined locations in the mountain.

In FIG. 3 there is illustrated a schematic temperature diagram whichshows the operation of the invention. In the curve a shows thetemperature distribution along the line A A in FIG. 2 in the originalcase without the supply of extra heat, and curve b the correspondingtemperature distribution with heaters coupled .in. As will be evident,it is possible, by means of the heaters according to the invention, to 1bringthe boundary area between the mountain and the air in the tunnel oron the outside up to a temperature above 0 C without significantlyheating large portions of the mass of rock and of the air at the side ofthe mountain.

According to experience, from 100 to 150 W/m is sufiicient to maintaineven the most exposed portions ice-free.

With a heating element which develops about 50 W a distance of about 70cm betw een the heaters in a square pattern will give in most instancesa sufficient yield.

That which is indicated here in the embodiment for tunnels also servessubstantially for exposed mountain areas, such as mountain cuttings andthe like. In certain instances, constructional-problems can occur withthe protection of leads and other projecting constructional componentsagainst mechanical stress, but this does not involve the principle ofthe invention. 1

Therefore, it is possible with the invention to procure an effective andreasonable frost-protection in tunnels, mountain cuttings and the likewhile maintaining installation and operative costs low. Besides, thearrangement according to, the invention is, by virtue of its simpleconstruction, pendable. By appropriate design of the heaters, possiblenecessary repairs can be made simple.

tightly up under the face. Preferably, the cloth material is fixedrelatively tightly stretched out between adjacent end pins of theheater. The cloth material 27 can be layed out in suitable widths of thepassage, for example, by laying out in the longitudinal direction of thetunnel and by overlapping along the edges in such a manner that it isensured that the water which trickles out from the rock face is conveyedalong the side of the cloth material which faces inwards to the side ofthe mountain. If desired, special fastening means can be used to securethe cloth material on the end pins 25, 26 just up under the bore holeand, at the same time, to provide a sealing off between the end pins andthe cloth material. If desired, there can also be obtained a fluidandgas-tight sealing between the adjacent and overlapping breadths of clothmaterial by sticking together the breadths of cloth material or inanother suitable way, but the latter is not regarded as necessary undernormal conditions, since a free overlapping is especially de- Referringto FIGS. 4, 5 and 6, a section ofa tunnel has heaters 20 which areconnected to each other in a star coupling by means ofcurrent-conducting means 21 shown in FIG. 1 by reference numerals 21a,21b and 210, so that there are correspondingly formed three separatecircuits which can be combined according to need. If desired, thecentral point in the star coupling can be connected to a fourth currentconductor so that the three circuits can be coupled in and coupled outindependently of each other.

In the preferred embodiment which is illustrated in FIGS. 2 and 3, theheater 20 consists of reinforcing steel having a diameter of 6-8 mm,while the current-conducting means 21 correspondingly consist ofreinforcing steel having a diameter of 12 mm.

In 'the rock face 22,.there is formed a bore 23 having a diameter of 35mm and a length of about 300 mm. In the bore 23, there is inserted in aheat-conducting moulding material, the heater 20. The heater 20, whichhas a total length of about 1,100 mm extends with endpins 25, 26 at theopposite ends about 50 mm outside the bore, while that within the borein which the all predominant length of the heater is received, extendsU-shaped in a double-folded loop 26 so that a concentrated heatingwithin the bore is achieved. Another advantage in position on the endpins 25, 26 and pushing this relatively 7 5 'material and the rock facelying within.

, archway,

usually sufficient.

The cloth material can be light-reflecting on that side of the clothmaterial which faces away from the tunnel archway. By means of such alight-reflecting lining of the tunnel archway,

light-technical advantages are achieved in a ready manner, in additionto the advantages which are obtained with respect to the drainage ofwater and the reduction of the need for heat for heating the rock facewhich is covered by the cloth material. By making the cloth material ofsuitable fiber-reinforced plastic material, sufficient strength can beobtained in the material to catch stones which possibly are loosened orbroken away from the covered mountain portion.

After the cloth material is arranged in position on the rock face whichis to be covered, the fixing end pins 25, 26 of the heater projectfreely outwards from the cloth material and are ready to have mountedthereon current-conducting means 21 The bar stumps can, if desired,.bepreformed so that the cloth material is held directly against the sideof the rock along the current-conducting means or can, if desired, aftermounting be pushed or pressed against the side of the mountain. In thisway, there can be formed more or less separate drain chambers betweenparallel series of current-conducting means having minimal aircommunication between neighboring chambers so as to provide a stationaryair layer between the cloth By allowing the current-conducting means toextend transversely of the tunnel there can be correspondingly formeddrain water conduit means between the tunnel archway and the clothmaterial in the said chambers between parallel series ofcurrent-conducting means. In the construction of FIG. 1, the rows ofcurrent-conducting means are within their respective spheres of thetunnel archway or are arranged in each of the current circuits mainly ina direction transversely of the tunnel. The current-conducting meanswhich extend along .the tunnel do not need to be pressed inwards againstthe rock face as are the transverse current-conducting means but canextend rectilinear ly or, if desired, slightly outwardly arched so as topermit the formation of drain water conduit means between the rows ofthe remaining current-conducting means.

By utilizing current-conducting means and heaters of reinforcing steel,an eflective support of the cloth material can be obtained and ofpossible loosened stones which are caught by the cloth material. (Evenrather large stone blocks can be caught by the network of reinforcingsteel which the currentconducting means and heaters form. Even if thenetwork of reinforcing steel is deformed or destroyed as a consequenceof such a block of stone comingloose from the tunnel archway, thefalling of the stone block down on to the roadway and the causing ofdamage can at any rate be prevented.)

With possible repairs, the current-conducting means can be readilyclipped off and welded on anew as required. If it is desirable, for oneor another reason, to install further heaters in the rock face inaddition to the originally mounted heaters, the latter can be readilyfreed without making substantial provisions in the original equipment.

During operation, there can be employed single phase or multi-pha'sealternating current having for example up to 48 V voltage. Theheaterscan be designed to yield respectively for example -1000 W allaccording to the heat need at the individual location. The controlequipment for the heating installation can be done quite simply and can,for example, be based on a thermostatic coupling. For example, there canbe utilized a thermostat or a combination of thermostats, which besidesreacting at the temperature of the air in the tunnel or in the open,also take account of the temperature at one or more predeterminedlocations in the mountain. if desired control of the connectionand'disconnection of the various circuits 21a, 21b and 210 can bepulsating, alternate or continuous current feed, all according to needand controlled by suitable known control means.

A distance between the heaters of about 50 cm has been found to beespecially favorable from a heat economic viewpoint. However, it isapparent that the distance between the heaters can vary according .todesire and need and correspondingly there can be employed stronger orweaker heat yields from each heater for example by employing thinner orthicker reinforcing steel in the heaters. If desired, provision can alsobe made for obtaining a certain heat emission from thecurrent-conducting means, but this heat effect is little relative to theheat effect from the heaters in that the reinforcing steel in thecurrent-conducting means can be dimensioned sufficiently liberallyrelative to the reinforcing steel in the heaters. I It will beappreciated that the true scope of the invention is not limited by theaforesaid embodiments which have been described purely by way ofexample. For instance, the invention can also embrace a device whichonly difiers from one described above in that the heating means arereplaced by insert means interconnected by metal rail means which simplyform a support network beneath the fluid-tight cloth facing material andare not connected to a source of electric current.

What I claim is:

1. In a process for the prevention of the formation of ice in tunnels,especially road and railway tunnels, and mountain cuttings and thelikeby the supply of heat from the outside to rock faces where ice formationnormally occurs, the improvement which comprises installing electricalheating means distributed in a self-supporting manner in individualbores formed in a rock face substantially at right angles to a boundarysurface with the air and heating a layer of rock between the air andrear-lying rock masses to a temperature higher than the temperature atsaid boundary surface and lower than the temperature at said rear-lyingrock masses, whereby the transport of heat from the latter towards saidboundary surface and from said layer of rock to said rear-lying rockmasses is substantially counteracted.

2. A process according to claim 1, which comprises placing the heatingmeans at a mutual distance of between 30 and 100 3. A process accordingto claim 2, wherein the distance is about 50 cm. Y

4. A process according to claim 1, which comprises spacing from butanchoring indirectly to the rock face a fluid-tight cloth facingmaterial by way of the heating means to form between said rock face andsaid facing material a liquid-conducting and temperature-barring layer.

5. A process according to claim 4, wherein the material is gas-tight.

6. A process according to claim 4, which comprises initially securing inthe rock face heating means having outwardly projecting fixing means andthereafter threading the facing material into position on said fixingmeans and finally ensuring facing that said facing material is incurrent-conducting connection with said fixing means.

7. A process according to claim 4, which comprises utilizing relativelyrigid current-conducting means between the distributed heating means tosupport the facing material.

8. A process according to claim 4, which comprises utilizing a facingmaterial having a light-reflecting surface directed outwardly from thecovered rock face.

9. A device which comprises insert means dimensioned for direct andalmost complete introduction in individual bores formed in a rock face,locating means for ensuring self-supporting mounting of said insertmeansin said bores, a fluidtight cloth facing material spaced from butanchored indirectly to the rock face by way of the insert means to formbetween said rock face and said facing material a liquid-conducting andtemperature-barring layer and metal rail means interconnecting saidinsert means to form 'a supporting network beneath facing material.

10. A device according to claim 9, wherein the metal wall means are madeof reinforcing steel.

11. A device according to claim 9, wherein the facing material has alight-reflecting surface directed outwardly from the covered rock face.

12. A device according to claim 9, wherein the facing material isgas-tight.

13. A device according to claim 9, wherein the insert means arepositioned at a mutual distance of between 30 and cm.

14. A device according to claim 13, wherein the distance is about 50 cm.

15. A device as set forth in claim 9 wherein said insert means is aheating means and which further comprises current-conducting meansinterconnecting said heating means to a source of electric current.

16. A device according to claim 15 further including a heat conductingmolding material about said heating means.

17. A device according to claim 15, wherein said heating means areenclosed in outer jackets of elastic heat-conducting material so as tobe self-supportingly receivable in their respective bores as a unit.

18. A device according to claim 17, wherein said heating means includean elastic shock-resistant portion for securing said means to the wallof a bore and for producing a heat-conducting contact with the bore.

19. A device according to claim 15 further including a fluidtight clothfacing material secured to said heating means in spaced relation to therock face to form between said rock face and said facing material aliquid-conducting and temperature-barring layer.

20. A device according to claim 19, wherein the currentconducting meanscomprise rigid metal rails arranged beneath the facing material in theform of a supporting network therefor.

21. A device according to claim 20, wherein the rigid metal rails aremade of reinforcing steel.

22. A device according to claim 19, wherein the heating means comprisemetal rod heating elements having a form selected from bar and loopshapes.

23'. A device according to claim 22, wherein the metal rod is U-shapedin a double loop with outer end legs projecting freely outwards to formfixing means in which the cloth material is threaded and to which thecurrent-conducting means are secured.

24. A device according to claim 22, wherein the metal rod heatingelements are made of reinforcing steel.

25. A device according to claim 19, wherein the material has alight-reflecting surface directed outwardly from the covered rock face.

26. A device according to claim 15, wherein the heating means arepositioned at a mutual distance of between 30 and 100 cm.

27. A device according to claim 26, wherein the distance is about 50 cm.

facing

1. In a process for the prevention of the formation of ice in tunnels,especially road and railway tunnels, and mountain cuttings and the likeby the supply of heat from the outside to rock faces where ice formationnormally occurs, the improvement which comprises installing electricalheating means distributed in a self-supporting manner in individualbores formed in a rock face substantially at right angles to a boundarysurface with the air and heating a layer of rock between the air andrear-lying rock masses to a temperature higher than the temperature atsaid boundary surface and lower than the temperature at said rearlyingrock masses, whereby the transport of heat from the latter towards saidboundary surface and from said layer of rock to said rear-lying rockmasses is substantially counteracted.
 2. A process according to claim 1,which comprises placing the heating means at a mutual distance ofbetween 30 and 100 cm.
 3. A process according to claim 2, wherein thedistance is about 50 cm.
 4. A process according to claim 1, whichcomprises spacing from but anchoring indirectly to the rock face afluid-tight cloth facing material by way of the heating means to formbetween said rock face and said facing material a liquid-conducting andtemperature-barring layer.
 5. A process according to claim 4, whereinthe facing material is gas-tight.
 6. A process according to claim 4,which comprises initially securing in the rock face heating means havingoutwardly projecting fixing means and thereafter threading the facingmaterial into position on said fixing means and finally ensuring thatsaid facing material is in current-conducting connection with saidfixing means.
 7. A process according to claim 4, which comprisesutilizing relatively rigid current-conducting means between thedistributed heating means to support the facing material.
 8. A processaccording to claim 4, which comprises utilizing a facing material havinga light-reflecting surface directed outwardly from the covered rockface.
 9. A device which comprises insert means dimensioned for directand almost complete introduction in individual bores formed in a rockface, locating means for ensuring self-supporting mounting of saidinsert means in said bores, a fluid-tight cloth facing material spacedfrom but anchored indirectly to the rock face By way of the insert meansto form between said rock face and said facing material aliquid-conducting and temperature-barring layer and metal rail meansinterconnecting said insert means to form a supporting network beneathfacing material.
 10. A device according to claim 9, wherein the metalwall means are made of reinforcing steel.
 11. A device according toclaim 9, wherein the facing material has a light-reflecting surfacedirected outwardly from the covered rock face.
 12. A device according toclaim 9, wherein the facing material is gas-tight.
 13. A deviceaccording to claim 9, wherein the insert means are positioned at amutual distance of between 30 and 100 cm.
 14. A device according toclaim 13, wherein the distance is about 50 cm.
 15. A device as set forthin claim 9 wherein said insert means is a heating means and whichfurther comprises current-conducting means interconnecting said heatingmeans to a source of electric current.
 16. A device according to claim15 further including a heat conducting molding material about saidheating means.
 17. A device according to claim 15, wherein said heatingmeans are enclosed in outer jackets of elastic heat-conducting materialso as to be self-supportingly receivable in their respective bores as aunit.
 18. A device according to claim 17, wherein said heating meansinclude an elastic shock-resistant portion for securing said means tothe wall of a bore and for producing a heat-conducting contact with thebore.
 19. A device according to claim 15 further including a fluid-tightcloth facing material secured to said heating means in spaced relationto the rock face to form between said rock face and said facing materiala liquid-conducting and temperature-barring layer.
 20. A deviceaccording to claim 19, wherein the current-conducting means compriserigid metal rails arranged beneath the facing material in the form of asupporting network therefor.
 21. A device according to claim 20, whereinthe rigid metal rails are made of reinforcing steel.
 22. A deviceaccording to claim 19, wherein the heating means comprise metal rodheating elements having a form selected from bar and loop shapes.
 23. Adevice according to claim 22, wherein the metal rod is U-shaped in adouble loop with outer end legs projecting freely outwards to formfixing means in which the cloth material is threaded and to which thecurrent-conducting means are secured.
 24. A device according to claim22, wherein the metal rod heating elements are made of reinforcingsteel.
 25. A device according to claim 19, wherein the facing materialhas a light-reflecting surface directed outwardly from the covered rockface.
 26. A device according to claim 15, wherein the heating means arepositioned at a mutual distance of between 30 and 100 cm.
 27. A deviceaccording to claim 26, wherein the distance is about 50 cm.